Stabilization of organic substances



Patented Amt. 3,, 1945 PATENT OFFICE I 2,373,049 STABIMZATION OF ORGANIC SUBSTANCES Charles 5. Peder-sen, lenns Grove, N. 3., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Deiaware No Drawing. Application February 5, 1943,

Serial No. 414,341

maims.

This invention relates to the stabilization of organic substances and particularly to thestabilization of such substances which are subject to deterioration caused by the action of molecular oxygen and catalyzed by metals and their compounds.

Many organic products, such as drying oils, rubber, petroleum products, photographic developers and synthetic unsaturated compounds, are readily attacked by oxygen and the resulting deterioration imparts undesirable qualities to them and eventually destroys their usefulness.

Signal success has been achieved in recent years, in the preservation of many organic-substances, by the discovery and use of compounds generically called "oxidation inhibitors or antioxidants. These agents, mostly oxidizable organic compounds, retard the auto-catalytic process. Since antioxidants are themselves oxidized in the course of time, as a result of auto-oxidation, the beneficial effect, obtained by their use, is not permanent and they protect the organic substances only so long as they are not rendered inactive. They are, moreover, very specific in action, each group of auto-oxidizable substances requiring a different type of antioxidant for the best results.

Vanadium, chromium, manganese, iron, cobalt, copper and their catalyticaly active compounds accelerate the rate of oxidation of many organic substances. For example, it is well known that copper compounds speed the formation of gum in cracked gasoline and the aging of rubber and that cobalt compounds promote the oxidation of drying oils. They also accelerate the oxidation of aromatic hydroxy and amino antioxidants, used to stabilize these oxidizable substances. Hence, these metal catalysts and the antioxidants are antagonistic in action, and the normal inhibiting effect of the latter is greatly'reduced in the presence of the former.

Metal compounds occur naturally in many organic products, but often in such slight traces as to cause very little harm. Their concentrations,

however, are frequently raised during the course ofhandling and utilizing the products; vessels and conduits, made of metals containing copper, etc., are used for storage and transportation, or ingredients, contaminated with metal compounds, might be added.

The harm done bythese extraneous catalysts may be prevented 'by at least three methods: (1) their removal by purification, but often this (Cl. M- M) '10 increased quantity of antioxidant required for adequate stabilizationfand (3) the suppression of the catalytic activity of the metal compounds by chemical means without physically removing them from the system.

It is an object of the present invention to retard the deterioration of organic substances caused by the action of molecular oxy en and promoted by the presence of certain metal cata-, I

lysts and their catalytically active compounds. ao Another objectis to render antioxidants, which are relatively ineifective in the presence of metal catalysts and their catalytically active compounds, efiective to inhibit the oxidation of oxidizable organic substances even' in the presence of metal catalysts and their catalytically active compounds. A further object is to provide a new class of metal deactivators which are efi'ectlve to render metal catalysts inactive to catalyze the oxidation of oxidizable organic substances containing or in contact with such metal catalysts. A more particular object is to inhibit the deterioration of petroleum hydrocarbons in the presence ofmetalcatalysts and their catalytically active compounds, Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with my invention which comprises adding to organic substances, normally subject to deterioration caused by the action of molecular oxygen, and containing a catalyst of the group of vanadium, manganese, cobalt, copper and their compounds, normally eifective t catalyze oxidation of said organic substances,

4:; metal deactivators in a small proportion sumcient to deactivate such catalysts, such metal deactivators being thioureas. having the formula wherein R represents hydrogen or an electronegative organic radical and salts of such thioureas. The organic substance also may and generally will contain an antioxidant which is normally effective to retard oxidation of the organic substance in the absence of the metal catalyst. I have found that such metal deactivators are capable of efiectively suppressing the catalytic activity of vanadium, manganese, cobalt, copper and their c'atalytically active compounds and hence will render such catalysts inefiective to catalyze the oxidation of the organic substance, including any antioxidant which may be present.

The organic substances, which may be treated in accordance with my invention, include fruit and vegetable juices, textile fibres, photographicdevelopers, antioxidants, synthetic unsaturated wherein the free valence is satisfied by hydrogen or an electronegative organic radical and may be used as the free compounds or as their salts. Where the thioureas are acidic, I may use their salts of bases, such as the salts of the alkali metals, ammonia or organic substituted ammonium bases. When the thioureas are alkaline in reaction, I may use their salts of acids including inorganic acids, as well as organic acids. General 1y, I prefer the free thioureas.

Representative electronegatlve organic radicals are aromatic, vinyl, allyl and guanyl. Substituted thiourea, in which the substituent is electropositive, such as amino and alkyl radicals, is excluded from within the scope of my invention. Preferably, the electronegative organic radical, in the substituted thiourea., is an arcmatic radical and particularly an aryl radical. By an "aromatic radica I mean one in which the free valence belongs to a carbon atom of a benzene ring, and which may contain non-hydro-- carbon substituents. By an aryl radical, I mean an aromatic radical which consists of the elements carbon and hydrogen. Also, preferably, the aromatic and aryl radicals, in the substituted thioureas, are of the benzene series, that is, contain only one benzene ring. The most desirable compounds appear to be thiourea. and N-phenylthiourea.

Definite operative concentrations of the metal deactivator in the organic substance cannot be specified for each cas as the quantity required is dependent upon the amount of metal catalyst present in the organic substance. The metal deto about 0.1%, based on the weight of the organic substance, will be sufflcient for most purposes, particularly when th organic substance ferent samples.

oxidant.

activator should be present in the proportion of is a liquid petroleum hydrocarbon, such as a gumforming hydrocarbon distillate of the character of cracked gasoline. In rubber, about 0.1% to about 1.0% will generally be employed.

The catalytically active metal and its compounds may be dissolved in the organic substance or suspended therein or may be in the form of metal in bulk in intimate contact with the organic substance. It. will be understood that, when I refer to an organic substance containing a catalyst, I mean to include those cases wherein the metal in bulk form is in contact with the organic substance as well as those cases wherein the catalytically active metal is dissolved or suspended in the organic substance.

The deactivators may be added to the oxidizable organic substances to be protected in any form and manner. They may be in solid or liquid form, mixed with other additional agents or dissolved in a solvent. They may be dissolved in the organic substance or dispersed therein in any suitable manner. They may be added to the finished organic substance or to the organic substance at any suitable stage in its manufacture.

The experimental results, obtained with compounds belonging to this class of deactivators, are given in the following tables.

In order to avoid confusion arising from a superabundance of data, gasoline has been selected as an example of an auto-oxidizable organic substance for the purposes of illustration. The samples of gasoline, used in the following tests, were either crackedgasolines or blends of cracked and straight-run gasolines, completely refined, but otherwise untreated with chemical agents, such as dyes, anti-knocks and antioxidants. Since gasoline is a mixture of variable composition, identical results are not obtained with dif- The magnitude of the effects is great enough, however, to render this difference relatively insignificant.

p-(n-Butyl) aminophenol, abbreviated BuBAP, has been chosen as a representative gasoline anti- The metals, present as catalysts, were employed as their oleates. The concentrations of the antioxidants and the metal deactivators are given in weight percent in gasoline. The concentrations of the metals are given in parts per million by weight of the metal, abbreviated P. P. M., rather than by weight of the metal compound.

The term stabilized gasoline is employed to denote gasoline to which has been added an antioxidant in sufficient quantity to significantly increase its induction period in the absence of added metal catalysts.

The accelerated method, used for determinining the induction periods given below, was the one described in J; I. E. C. 25, 397 (1933). It consists in heating cc. of gasoline at 100 C. in a 1 liter Pyrex flask containing pure oxygen. The internal pressure is observed every 10 minutes by means of a manometer attached to the system. The elapsed time, from the start of the test until the gasoline begins to absorb oxygen at the rate-of 10 cc. per 10 minutes or higher, as shown by the fall in internal pressure, is taken as the induction period. It has been found that the induction period, obtained by this method, although greatly shortened, is a fairly accurate measure of the relative stability of gasoline under normal storage conditions.

It will be observed that the catalytic action of copper is counteracted to a. greater or lesser ex tent by the diflercnt derivatives of thiourea containing an electronegative radical. The alkylsubstituted compound is practically without effeet, the alkyl radical being electropositive.

The eflect of another deactivator is shown in Table II.

Table I] Cone. Gone. 7 Ind. No BuPAP cu Deactivator Com period Wt. Wt. Mmpercent P. P. M. percent was 1.-., 0.0 0. None 130 2.--. 0.002 0.0 485 3--.. 0.002 1.0 do 50 4. 0.002 1.0 N-(il-aminophenyb- 0.0025 490 thiourea.

The relationship between the concentration of thiourea and the induction period is shown in Table n1.

' Table III Cone. Conc. Conc. Induction BuPAP cu Thiomea period Wt. cent P. P. M Wt. cent Mmaea' It will be noted that very little advantage is gained by adding more than the quantity of deactivator required for complete deactivation. The concentration curves, obtained with these compounds, instead of being rectilinear as for antioxidants, are logistic and the efiects of antioxidants and deactivators are synergistic.

It will be understood that the experiments and tests,hereinbefore given,have been given for illustrative purposesonly. Many variations and modiflcitions can be made in my invention-without .de-

parting from the spirit or scope thereof. Themetal deactivators of my invention can be employed in other organic substances, the metals may be present in other forms and other com- .referred to hereinbefore. While I I have disclosed the use of single metal deactivators, it will Besides many others, the following compounds are within the scope of my invention:

N-phenylthiourea N-(o-tolyl) thiourea N- (p-tolyl) thlourea N- l-naphthyl) thiourea N- (2-naphthyl) thiourea N- 4-ethoxyphenyl) thiourea N (Z-methoxyphenyl) thiourea N-xylylthiourea N o-cymyl) thiourea N- (m-tolyl) thiourea N (o-biphenyl) thiourea N p-biphenyl) thiourea It will be apparent that, by my invention, I am able to efiect the stabilization oforganic substances susceptible to the harmful action of molecular oxygen catalyzed by vanadium, manganese, cobalt, copper and their catalytically active compounds. This stabilization may be accomplished, in accordance with my invention, by the addition of metal deactivators, either alone or in combination with an amount of an antioxidant sumcient to stabilize the substance in the absence of metal catalysts. It is often technically and economically unfeasible to counteract the catalytic eiiects of such metals by means of an antioxidant alone. I believe that the metal deactivators of my invention function by forming very stable complexes with the metals. which complexes are catalytically inactive. It

- appears that the metal deactivators of my invention, in general, are not antioxidants. However, my invention is not to belimited by any theory as to the manner in which the metal deactivators pounds, within the broad scope of my invention, I may be substituted for the compounds specifically be apparent that mixtures of two or more metal deactivators of my invention may be employed if desired. 7

function to produce the resu1ts.-

I claim:

1. A compositioncomprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a member of the group consisting of thioureas having the formula wherein R represents a member of the group consisting of hydrogen and an electronegative organic radical and salts of such thioureas.

2. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese. cobalt, copper and their compounds, normallyefiectiveto catalyze oxidation of said organic substance, and having incorporated.

therein a metal deactivator in a small proportion .suflicient to deactivate said catalyst, said metal deactivator being a thiourea having the formula R-NH- -NHQ wherein R represents a member of the group consisting of hydrogen and an electronegative organic radical.

3. A composit on comprising an organic substance, normally subject to deterioraton caused by the action ,of molecular oxygen, containing a catalyst of the group consisting of vanadium,

4. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being thiourea in which a single hydrogen has been replaced by an electronegative organic radical.

5. A composition comprising an organic substance, normally subject to deteriorat on caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese. cobalt, copper and their compounds, normally efiective to catalyze oxidation'of said organic substance, and having incorporated therein a metal deactivator in a small proport on sufficient to deactivate said catalyst, said metal deactivator being thiourea in which a s ngle hydrogen has been replaced by an electronegative aromatic radical. i

6. A composition comprising an organic substance, normally subject to deteriorat on caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese. cobalt, copper and their compounds, normally eifective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proport on suflicient to deactivate said catalyst, said metal deactivator be ng thioureain which a single hydrogen has been replaced by ,an aryl radical.

7.' A composition comprising an organic substance, normally subjectto deteriorat on causedby the action of molecular oxygen, containing a catalyst of the group consisting of vanadium,.

manganese. cobalt, copper and their compounds. normally effective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proport on suflicient to deactivate said catalyst, said metal deactivator being thiourea in which a single hydrogen has been replaced by an. electronegative aromatic radical of the benzene series.

8. A composition comprising an organic substance, normally subject to deteriorat on caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said organic substance; and having incorporated therein a metal deactivator in a small proport on sufficient to deactivate said catalyst, said metal deactivator being thiourea in which a single hydrogen has been replaced by an 'aryl radical of the benzene series.

9. A composition comprising an organic substance, normally subject to deteriorat on caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium,

manganese. cobalt, copper and their compounds,

normally effective to catalyze oxidation of said organic 'substance, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said inetal deactivator being N-phenylthiourea.

10. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen; containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds,

normally effective to catalyze oxidation of said orwherein R represents a member of the group consisting of hydrogen and an electronegative organic radical and salts of such thioureas.

11. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and a small proportion of an antioxidant, normally. efiective to materially retard such deterioration in the absence of said catalyst but which is less eifective in the presence ofsaid catalyst, and having incorporated thereina metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being thiourea.

12. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, v

manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less effective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being thiourea in which a single hydrogen has been replaced by an electronegative organic radical.

13. A composition comprising an organic substance, normally subject to deterioration caused by the action .of molecular oxygen, containing a catalyst of the group consisting of vanadium,

manganese, cobalt, copper and their compounds normally efiective to catalyze oxidation of said organic substance, and a small proportion of ar antioxidant, normally effective to materially retard such deterioration inthe absence of said catalyst but which is less effective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being thiourea in which a single hy-- drogen has been replaced by an electronegative aromatic radical.

14. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containinga catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less eflective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufflcient to deactivate said catalyst, said metal deactivator being thiourea in which a single hydrogen has been replaced by an electronegative aromatic radical of the benzene series.

15. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium.

manganese, cobalt, copper and their compounds.

vanadium, manganese, cobalt, copper and their compounds, normally eflective to catalyze oxidation or said petroleum hydrocarbons, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a member of the group consisting of thioureas having the formula V wherein R represents a member of the group.

consisting of hydrogen and an electronegative organic radical and salts of such thioureas.

17. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally efl'ective to catalyze oxidation 01' said petroleum hydrocarbons, and having incorporated therein a metal deactivator in a small proportion sumcicnt to deactivate said catalyst, said metal deactivator being thiourea.

18. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally eflective to catalyze oxidation of said petroleum hydrocarbons, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being N-phenylthiourea.

19. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally eilective to catalize oxidation of said petroleum hydrocarbons, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less efiective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a member of the group consisting of thioureas having theformula RNHCVNH1 wherein R represents a member of the group consisting of hydrogen and an electronegative organic radical and salts of such thioureas.

20. A composition comprising gasoline, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of vanadium, manganese, cobalt, copper and their compounds, normally effective to catalyze oxidation of said gasoline, and having incorporated therein a metal deactivator in a small proportion sufl'icient to deacitvate said catalyst, said metal deactivator being a member of the group consisting of thioureas having the formula ,R-Nllfi-Nliz wherein R represents a member of the group consisting of hydrogen and an electronegative organic radical and salts of'such thioureas.

CHARLES J. PEDERSEN. 

